More broadly, Mr Buttigieg urged Americans to move beyond the divisive politics of the Trump era to embrace a more inclusive, unifying approach.

"Politics at its worst is ugly," he said.

"But at its best, politics can lift us up. It is not just policymaking. It is moral. It is soulcraft. That's why we're in this."

Voters saw Mr Buttigieg in the more moderate lane of the Democratic field, and he flourished early with a top finish in the Iowa caucuses and a close second place finish in New Hampshire.

Bernie Sanders holds a campaign rally in Los Angeles.
Picture:
PA

But as the race moved to more diverse states, less dependent on college-educated voters, Mr Buttigieg struggled.

After his unexpected rise to contention in Iowa and New Hampshire last autumn, Mr Buttigieg became the target of Massachusetts Senator Elizabeth Warren for the high-dollar fundraisers he was hosting, notably one in a wine cave in California.

Minnesota Senator Amy Klobuchar also went at Mr Buttigieg in the months before the caucuses for lacking national experience.

She noted that he had lost his only statewide race as a candidate for Indiana treasurer in 2010, while she had won three statewide terms in Minnesota in part by carrying Republican-heavy regions.

He had modelled his campaign somewhat on that of former president Barack Obama, who won the 2008 Iowa caucuses largely based on a message of unity and by drawing in a healthy bloc of first-time caucus participants, often the key in a crowded, high-turnout contest.

Democratic strategist David Axelrod said "the Pete Buttigieg story isn't over,” adding: "He's 38 years old. He's vaulted himself into the national conversation.

"He obviously has work to do on some things - some weaknesses we've seen in this election - but whenever there is a conversation again about Democratic candidates, he'll be in that conversation.

"And that's a remarkable achievement, given where he started a year ago."